LAS VEGAS, Nev. - The key weapon in TV broadcasters' fight with Internet video upstart Aereo is something inelegantly known as a dongle.

The miniature TV antenna picks up free, mobile broadcast signals. It attaches to iPhone and iPad power ports and extends about 7 inches, allowing users to view live local TV channels at not-quite-high-definition quality.

The device scans the airwaves for signals with the help of an app. The antenna doesn't sap a user's data plan or rely on Wi-Fi signals, but it does need to be recharged.

"If you're at a ball game or a Starbucks and everyone's trying to access the news, you're not going to get (video stoppages)," says Karen McCall, a marketing representative with Dyle Mobile TV, the venture backing the devices.

The dongles are on display at the annual gathering of broadcasters, the NAB Show, taking place this week at the Las Vegas Convention Center. Dyle says it plans to release units for Android devices soon.

Dyle is a coalition of 12 major broadcasters and networks such as Fox and NBC. The networks, along with ABC and CBS, are waging a legal fight against Aereo, a service that pulls down broadcast station signals with thousands of tiny antennas and sends the signal to mobile devices or computers over the Internet. Aereo users don't require a dongle, just a wireless Internet or cellphone connection.

Broadcasters contend that Aereo illegally steals signals from the air without paying for the rights before reselling them to customers. Aereo has prevailed so far. It won a preliminary ruling in an appeals court last week that allowed it to continue offering its service in the New York City area. It plans to expand to Boston, Chicago, Philadelphia, Washington and 18 other U.S. markets this spring.

Dyle began selling its dongles, made by companies such as Elgato and Escort, late last year on Amazon.com.

Compared to the $8-per-month streaming service by Aereo, the price seems high, but the dongles have the backing of major broadcasters.

The Elgato and Escort devices were designed before Apple reduced the size of the power ports on its newer iPhones and iPads. As a result, people who use the latest iPad and iPhone 5 will need to employ an adapter, which can make the contraption extend somewhat precariously.

The gadgets receive signals only from stations that specifically broadcast to mobile devices. So far, the dongles will work for the signals from 116 stations in 39 markets including New York, Los Angeles and Chicago. Signals come from affiliates of NBC, CBS, Fox, Univision and Telemundo, among others.